This one is pretty basic, but can be useful if you're like me and find it difficult to find the actual originals of the pictures you're browsing. If you pick the Finder as the application to launch when double clicking on a picture (in the iPhoto preferences), it will open a Finder window with the picture you double clicked selected. Kinda obvious, but I wasn't sure if it would work before trying it.

[Editor's note: Clearly this is the brute force method, but it's easier on hard drive space than my method - I just drag the image to the desktop and create a copy instead of rooting around in the Finder.]